The present invention relates to water treatment systems, and more particularly to an electronic driver or ballast for an ultraviolet household water treatment system.
Household water treatment systems have gained widespread popularity, particularly in areas with less-than-ideal potable water. A household system or unit is mounted on a single tap to selectively treat water flowing through the tap. Treatment may include filtration, irradiation, or both. The most effective water treatment systems include ultraviolet (UV) irradiation to sterilize the water stream. It is well known that such UV treatment kills bacteria and viruses with an extremely high degree of reliability. The water to be treated is routed through a container, and a UV light source within or adjacent to the container directs UV light through the water stream.
A first issue with UV water treatment systems relates to intensity control of the UV bulb. At least three factors are considered in determining the intensity of the UV light. First, it is desirable to operate the bulb at a relatively high intensity to achieve the maximum "kill rate" when water is flowing. Second, it is desirable to never extinguish the bulb, for example as one might be tempted to do when water flow stops, because of the start-up lag in bringing the UV intensity back up to treatment intensity when water flow is detected. Third, it is desirable to reduce bulb wattage or power when water flow stops to avoid excessive warming of the water "stagnated" within the treatment chamber.
Prior artisans have accommodated these considerations by designing bulb intensity control circuits capable of selectively driving the bulb at relatively high and low intensities. One such circuit is illustrated in U.S. Pat. No. 5,324,423 issued Jun. 28, 1994, to Markham and entitled UV BULB INTENSITY CONTROL FOR WATER TREATMENT SYSTEM. When water is flowing, as detected by a flow switch, the bulb is operated at high intensity to achieve the desired kill rate. When water flow stops, the bulb is operated at a lower intensity to avoid excessive warming of the water and to prevent extinguishing of the bulb. While the Markham circuit is a significant advance in the art, it is not without its drawbacks. The inductive ballast is more expensive and less efficient than desired. Further, the ballast is relatively heavy and noisy.
A second issue with water treatment systems is the possibility of electrical shock to a user. While the risk is low, the consequences can be serious because the systems plug directly into the household line voltage, which is 110 volts in the United States and varies from 100 volts to 264 volts throughout the world.
A third issue with water treatment systems is the variance in design from country to country. As noted in the preceding paragraph, line voltage can vary from 100 volts to 264 volts. Additionally, line frequency varies from 50 Hz to 60 Hz. Consequently, the electronics package of a water treatment system must be custom tailored to the line voltage/frequency combination for that country. This leads to design, manufacture, and inventory problems.